[Dune] Re: Notification from Dune

[Oliver Sander]

Hi Dune!
For me this is currently not an urgent issue, because I have long
ago written a wrapper around the ReferenceElements class that
corrects the inconsistencies in the ordering for me.  It goes
without saying that this is not an elegant solution, but it works
for me(TM).

The reason why I never just went out and fixed the problem is that
the reference cubes are really constructed through an algorithm
for all dimensions at once, and I never had the nerve to try and
understand that.  A second consequence is that I suppose that
there are similar problems with 3d cubes.  I never checked because
I don't use cube grids a lot.

My bottom line is: of course I would like to have this fixed
rather sooner than later.  On the other hand, it's not urgent.
I think generally Christian is right in saying that one should
not have semantic changes once an official version is released.
However relying on the ordering of the vertices of faces is a
rather obscure feature and I think hardly anybody uses that
anyways.

--
Oliver

************************************************************************
* Oliver Sander                ** email: sander at mi.fu-berlin.de        *
* Freie Universität Berlin     ** phone: + 49 (30) 838 75217           *
* Institut für Mathematik II   ** URL  : page.mi.fu-berlin.de/~sander  *
* Arnimallee 6                 ** -------------------------------------*
* 14195 Berlin, Germany        ** Member of MATHEON (www.matheon.de)   *
************************************************************************

On Wed, 18 Oct 2006, Christian Engwer wrote:

> Hi Dune,
>
> I am the one who marked this task 1.0
>
>> FS#120 - Inconsistent numbering of the vertices of the reference quad
>> User who did this: - Robert Klöfkorn (robertk)
>>
>> ----------
>> If this is not considered critical, I would like to mark this task for
>> post 1.0.
>
> We discussed this issue in Stuttgart and we decided, that this issue
> must be solved before 1.0 in the one ore other way. Oliver complains,
> that the faces in the reference quad are oriented with some normal
> vectors pointing outwards and some pointing inwards.
>
> We agree, that it would be nice to have all normalvectors pointing
> inwards (like in the reference triangle). The current orientation
> arises from the fact, that the reference cubes are constructed via
> tensor product.
>
> None of us three, participating in the discussion, wrote the code or
> knew the details, so we could not say how difficult it would be to
> change this behaviour.
>
> If it is managable, we should do this change before 1.0, because
> changing the semantics of the reference cube after 1.0 would be a
> really bad idea; the api would stay the same and no user whould be
> warned to change his code. Really strange and hard to find errors
> would be the result.
>
> If it is to hard to implement we should just close the bug as "won't
> fix".
>
> Anyway we should come to a decission before 1.0, because changes to
> the semantics of the reference elements after 1.0 are dangerous.
>
> Perhaps Peter can say a little bit about the reasons for this
> numbering and about the required amount of work for the demanded
> changes.
>
> Cheers Christian
>
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